Fan arrangement for pollution control

ABSTRACT

A rotary fan arrangement mounted on a structure such as a smokestack creates a plume of ambient air concentric with the pollutants rising upwardly from the stack, the plume of air serving both to dilute the pollutants and to carry the pollutants aloft. In one embodiment, the fan arrangement includes hinged blades and, in another, centrifugally erected sail rotors.

United States Patent Feldman 1 Feb. 22, 1972 [54] FAN ARRANGEMENT FORPOLLUTION CONTROL [72] Inventor: Lewis Feldman, 15 Ireland Place,Amityville, N.Y. 11701 [22] Filed: Jan. 6, 1969 [21] Appl.No.: 789,118

[52] US. Cl ..98/58, 110/184, 239/14, 418/152 [51] Int. Cl ..A23C 9/10[58] Field of Search ..98/58, 60; 239/2, 14; 230/96; 110/184 X; 418/152[56] References Cited UN lTED STATES PATENTS 458,996 9/1891 Bullock..230/96 629,019 7/1899 Thomas .....230/96 1,130,733 3/1915 Hoke..230/96 2,282,256 5/1942 Smelik ..98/58 X 3,115,820 12/1963 Adelt..98/60 FOREIGN PATENTS OR APPLICATIONS 907,852 10/ 1962 Great Britain..98/58 OTHER PUBLICATIONS Science & Mechanics p. 92'93 Dec. 1955Primary Examiner-William E. Wayner AnomeyLarson, Taylor and Hinds [5 7]ABSTRACT A rotary fan arrangement mounted on a structure such as asmokestack creates a plume of ambient air concentric with the pollutantsrising upwardly from the stack, the plume of air sewing both to dilutethe pollutants and to carry the pollutants aloft. In one embodiment, thefan arrangement includes hinged blades and, in another, centrifugallyerected sail rotors.

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ATTORNEY 5 PATENTEBFEB 22 I972 SHEET 8 0F 4 'mvm fons LEWlS FELDMAN m cycz/zsa ATTORNEYS FAN ARRANGEMENT FOR POLLUTION CONTROL FIELD OF THEINVENTION The present invention relates to the control of pollutants inthe air and more particularly to a fan arrangement for effecting suchcontrol.

Background of the Invention The problem of air pollution, particularlyin urban areas, has drastically increased in seriousness in recent yearsand a great deal of national attention, both public and private, hasbeen focused thereon. A significant cause of air pollution is smoke andother air pollutants discharged into the atmosphere from factories andthe like. Relatively normal pollution conditions in the atmosphere canbe greatly exacerbated by a phenomenon known as an atmosphericinversion.

To explain, it is noted that there is a concept in meteorology ofadiabatic lapse rate which refers to the rate of decrease with altitudeof the temperature of an ideal bubble of air moving from one altitude toanother without mixing or heat exchange. This rate is 5.4" F. per 1,000feet of altitude for dry air and somewhat less for moist air, the exactvalue depending on the humidity. An atmosphere with an adiabatic lapserate is roughly neutrally stable with respect to vertical mixing.Steeper temperature drops-referred to as superadiabatic lapse rates-areunstable whereas shallower drops are stable, the stability increasing asthe lapse rate decreases from adiabatic. Lapse rates less than adiabatichave been referred to as inversions although such rates may perhaps bemore accurately referred to as inversions of the potential temperature,the term inversion being more commonly used to refer to an increase intemperature with altitude. Such a meteorological condition is extremelystable and resists the upward flow of stack effluents. Thus noxiouseffluents from various sources in the area are not able to penetrate theatmosphere as well as under normal conditions and hence pollution of theatmosphere overlying the area is caused. As a consequence of suchatmospheric inversions severe pollution problems, such as occur forexample almost continuously in the Los Angeles basin, may result.

One approach taken in attempting to alleviate such conditions is theutilization of very tall stacks. Such stacks may actually carry thewastes to altitudes above the inversion and thus when the wastes aredumped into the atmosphere they cannot return to altitudes justoverlying the area because of the superstability of the air in thevicinity of the inversion and thus mixing of the waste with the air of,the atmosphere takes place above the inversion layer. There are a numberof obvious drawbacks to the use of such stacks among which is the ratherprohibitive cost thereof.

Another related problem in which very tall stacks have been used in anattempted solution is that of providing dilution of poisonous stackeffluents so that when these materials reach ground level again aftercirculating in the surrounding air they are of sufficiently lowconcentration that any untoward effects are avoided. This problemoccurs, for example, in fertilizer plants wherein during processingfluorides are generated in the stack effluents. When these fluoridesreturn to earth in agricultural areas even very low concentrationsthereof can kill crops. For this reason such plants are generallylocated in very isolated regions and employ very tall stacks to ensureadequate mixing of the stack effluents with the ambient air before theplume from the stack can touch the ground.

SUMMARY OF THE INVENTION In accordance with the present invention astream of pollutants issuing from a smokestack or the like is controlledby means for creating an envelope of air around the pollutants thecross-sectional area of the air envelope being greater than thecross-sectional area of the stream of pollutants. The air envelope orplume so created, by surrounding the plume of pollutant, will ensurethat the pollutant has risen to a relatively high altitude beforediffusing through the air plume into the atmosphere. Further, thepollutant will be diluted as it diffuses through the air plume.

In a relatively simplified embodiment of the invention a fan arrangementof generally conventional form is provided which includes a series ofblades rigidly secured to a rotary hub. However, the blades of fans soconstructed will experience large bending moments which may cause thearrangement to be unsatisfactory for many applications. Moreover, fanblades advancing into the wind during rotation will be subject to agreater than average aerodynamic force while the retreating blades aresubject to a lesser force. The asymmetry of the aerodynamic forces onthe blade will produce a moment which will be transmitted to the stack.In addition, because each blade is alternately advancing and retreating,the load on the individual blades oscillates between a maximum and aminimum value.

It has been found that the effectiveness of the fan plume in dilutingthe stack plume increases as the size of the fan plume increases andthus for optimum effectiveness fan arrangements of very large diameterare desirable. However, all of the effects discussed above, the rootbending moment, the asymmetry of the air forces on the fan blades andthe oscillatory load thereon, increases rapidly with increasing fandiameter. For this reason the use of one of the more specialized fanarrangements of the invention discussed hereinbelow is generally to bepreferred.

In one embodiment the fan blades are hinged in a manner similar to theblades of a helicopter and a number of the problems discussedhereinabove are eliminated. This embodiment may still present drawbacksin providing stowage of the blades, it being desirable to stow theblades during high wind conditions when the fan is not needed and damagemay result to the blades or to the stack because of the presence of thefan, where the diameter of the fan blades is to be very largeQIn anotherembodiment the rotor blades are flexible and are deployed and tensionedby the centrifugal force on tip weights affixed to the ends of theblades. In a stowed position the blades are wrapped around amotor-driven spool and the tip weights are released to deploy the bladesupon rotation of the spool.

In yet another embodiment of the invention an auxiliary stack arrangedconcentrically with the main stack is used in place of the fan-typedevices discussed hereinabove to create the plume or jet of air whichsurrounds the plume of pollutants.

The control arrangement of the invention will provide penetration of theinversion layer in a manner similar to a tall stack. The use of thecontrol arrangement obviates the need for stacks of great height andrelatively short stacks may be utilized therewith. As stated, theouter'plume of air created thereby serves both to carry the waste plumealoft as well as to dilute this plume and thus the control arrangementof the invention may be used advantageously in situations such as thosedescribed above where it is desired to prevent poisonous effluents fromreturning to earth in other than a very dilute form. By carrying thewaste plume aloft and by diluting the waste plume through mixing thecontrol arrangement of the present invention provides a means forhandling poisonous stack effluents in a satisfactory manner.

It is noted that certain stacks eject material that has little or nobuoyancy in the atmosphere and thus propulsion of the effluents must beaccomplished by mechanical means. Such a process can be made moreeconomical and more effective by use of the control arrangement of theinvention.

It is noted that in accordance with a further feature of the presentinvention the directionality of the waste plume can be controlled bytilting of the plane of the blades of a fan arrangement such that theplume is ejected in a favorable direction, so that in calm weather, forexample, the plume can be aimed in the least objectionable direction andin windy weather the untoward effects of winds can be reduced throughselective orientation of the plume.

Other features and advantages of the present invention will be set forthin or apparent from the detailed description found hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representationof a control arrange ment in accordance with the present inventionillustrating the operation thereof;

FIG. 2 is a perspective view of an arrangement similar to that of FIG. 1wherein wind protection is provided;

FIG. 3 is a view similar to FIG. 1 wherein the fan blades are hinged toprovide stowage thereof;

FIG. 4 is a top view ofa presently preferred embodiment of the inventionwherein the details of a hinging arrangement for one of the fan bladesis shown;

FIG. 5 is a side view partially in section of the embodiment of FIG. 4;

FIG. 6 is a top view of a further preferred embodiment of the presentinvention wherein the fan blades are flexible and are shown in a stowedposition;

FIG. 7 is a side view, partially in section and partially broken away,of the embodiment of FIG. 6 with one of the blades shown in an unfurledposition;

FIG. 8 is an overall view of the embodiment of FIGS. 6 and 7 with two ofthe fan blades being shown in an unfurled positron;

FIGS. 9 and 10 are top and side elevational views of a furtherembodiment of the invention; and

FIGS. 11 and 12 are top and side elevational views of yet anotherembodiment of the invention wherein a fan arrangement is not used, aportion of FIG. 12 being shown in section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, aschematic representation of the invention, as incorporated in anenvironment including a factory complex denoted F having a smokestack S,is shown. In accordance with the invention a fan device 10 is mountedatop stack S for controlling a stack plume, generally denoted 12,issuing therefrom. Fan ,10 is preferably constructed in accordance withthe embodiments of FIGS. 4 and 5 or ofFIGS. 6 and 8 discussedhereinbelow but may in a simplified form thereof merely comprise aseries of rigid blades 14 mounted for rotation about the stack opening.A motor 16, also conveniently mounted atop stack S, may be used to drivea central hub 18 from which the blades 14 extend. The motor 16 and hub18 may be interconnected as described hereinbelow regarding FIGS. 4 and5. Reference is also made to FIGS. 9 and 10 which illustrate in moredetail a suitable rigid blade arrangement. Blades 14 rotate in a planegenerally perpendicular to the longitudinal axis of the stack S andthereby create a generally upwardly directed plume of ambient airdenoted 20 which surrounds stack plume 12. Thus stack plume 12 isenveloped by the outer cylindrical plume of air 20 and is carried aloftthereby. As discussed hereinbefore by carrying the stack plume aloft inthis manner the deleterious effects thereof can be significantlydecreased.

The use of rigid blades such as blades 14 of FIG. 1 presents a number ofproblems as was discussed above. Certain of these problems,specifically, those caused by or heightened by the presence of wind, canbe combatted to some extent through the addition ofa wind protectionshroud such as that shown in FIG. 2. In FIG. 2, wherein elementscorresponding to similar elements in FIG. 1 have been given likenumbers, there is shown a shroud 19 which comprises an open cylinderconcentric with the stack S and surrounding the blades 14. The shroud 19is connected to the stack S through spiders 19a so that the blades 14can rotate within the protective walls of the shroud 19. Although suchan arrangement serves to reduce the wind effects and improve theperformance of the fan as well as reduce the size of fan required anumber of disadvantages result from the use ofa shroud. For example, asthe size of the fan required increases the cost and weight of the shroudincrease correspondingly. It will be appreciated that the wind load ofthe shroud itself on the stack becomes prohibitive for larger diameterfan blades.

FIG. 3 shows what may be regarded as a second embodiment of theinvention wherein the fan blades are hinged to permit stowage thereof.In high winds such as those of hurricane force a fan is unnecessarybecause of the rapid dilution of the stack plume by the tremendousamounts of air circulated by the high velocity wind. Under thesecircumstances the blades are preferably stowed out of the wind todecrease the forces the fan and the stack must withstand and thus toimprove the overall safety of the installation. The embodiment of FIG..3 is generally similar to that of FIG. 1 and corresponding elementsthat have been given the same reference numerals with primes attached.Blades 14' are hinged at 21 to permit folding thereof to stowedpositions alongside stack S as shown. In the stowed positions thereof,blades 14 may be secured to stack S, by suitable means such as a clamp22 extending outwardly from the stack S, to prevent fluttering of theblades in high winds. I

Although simple hinges providing pivoting of the blades between thehorizontal, operative positions and the vertical, stowed positions maybe utilized, hinge 21 is preferably of the form shown in FIGS. 4 and 5.The helicopter-type mounts of FIGS. 4 and 5 provide pivoting of theblades in both vertical and horizontal planes and thus eliminate thebending moment at the root of the blades and reduce the oscillatory loaddue to wind.

Referring to FIGS. 4 and 5 a stack 24 includes an upper stack opening 26about which is mounted a fan arrangement generally denoted 28. Agenerally cylindrical hub 30 is mounted for rotation by bearingsindicated at 32 and includes a plurality of blades 34 (one of which isshown) extending outwardly therefrom. A motor 36 mounted on stack 24 bysuitable means (not shown) drives a pinion 38 which engages a gear track40 located around the internal circumference of a lower portion of hub30. Thus rotation of pinion 38 will cause rotation of hub 30 and,consequently of blades 34.

Blade 34 is attached to hub 30 through a flapping hinge 42 and a lagginghinge 44. Flapping hinge 42 is formed by a pin 46 which extends througha tongue member 48 received in an outwardly extending yoke member 50 ofhub 30. Pin 46 permits pivoting of blade 34 about the axis formedthereby in a vertical plane. Lagging hinge 44 is similarly formed by apin 52 which joins upper and lower portions ofa yoke member 54 to an endportion of blade 34 received therebetween. Yoke member 54 and tonguemember 48 are both part of an intermediate connecting member 56 andextend outwardly from opposite sides of member 56 as shown. Lagginghinge 44 provides pivoting of blades 34 in a horizontal plane.

Damper devices 58 and 60 may be utilized under certain circumstances todamp oscillations about hinges 42 and 44. Damper 58 is mounted on theside of yoke member 50 of hub 30 and includes an arm 62 attached tointermediate member 56 as shown. Similarly, damper 60 is mounted atopintermediate member 56 and includes an arm 64 attached to blade 34.

Although the embodiment of FIGS. 4 and 5 provides a number of advantagesas compared with a rigid blade or a simple hinged blade arrangement,such an arrangement may be undesirable where large radius fans are to beused. For example, the height of the stack required can, as stated, bereduced by the use of a fan and in some instances may be less than theradius of the fan. It is obvious that where the radius of the blades isgreater than the height of the stack the blades cannot be stowedalongside the stack as shown in FIG. 3. The embodiment of FIGS. 6 to 8provides ready stowage of the blades without regard to length as well asthe advantages of the embodiment of FIGS. 4 and 5.

Referring to FIGS. 6 to 8 a stack includes a central opening 72 aboutwhich is mounted a flexible fan blade arrangement generally denoted 74.The fan blades are formed by flexible members 76 which are preferablyconstructed of a fabric such as sail material and thus the blades 76 maybe conveniently referred to as sail rotors." Blade 76 is secured to aspool member 78 directly mounted on a motor-driven rotor 80 (see FIG.6). Bearings indicated at 82 and 84 permit rotation of bladeecarryingrotor 80 with respect to stack 70. Rotor 80 may also be driven by apinion and gear track arrangement such as described hereinbefore inconnection with the embodiment of FIGS. 3 and 4. As shown, rotor 80 ispart of a motor drive arrangement which includes a stator 81 affixed tothe stack.

An outer shield 86 is journaled to stack 70 by means of bearingsindicated at 88 and 90 so that the shield 86 is may also rotate withrespect to stack 70. Shield 86 is generally cylindrical in form althoughrounded at both ends and includes an upper central opening 92 to permitpassage of gaseous wastes issuing from the stack 70 therethrough.

Sail rotor blades 76 are preferably formed with a straight leading edge76a and a trailing edge which may be straight, convex or concave, aconvex trailing edge 76b being shown. A tip weight 94 individual to eachblade 76 aids in deploying the blades upon rotation of spool 78. Detailsof the construction of the sail rotor blades and the tip weights and themanner of attachment of the tip weights to the blades and of the bladesto the spool may be found in my copending application Ser. No. 789,328entitled Improvements in Flexible Rotor Devices and filed concurrentlywith the present application. Tip weights 94 are located outside shield86 and slots in shield 86 permit blades 76 to be affixed to the weights94. Weight 94 is broken away in FIG. 7 to show slot 96. Blades 76 arewrapped around spool 78 in their inoperative or rest states as indicatedin FIG. 6. Under these conditions tip weights 94 are each clamped to theshield 86 by a clamp 98. The clamps 98 can take a number of forms but asshown merely comprise first and second opposed spring members 100 and102 which capture the tip weight 94 therebetween. The biasing forceofsprings 100, 102 is such that upon rotation of spool 78 thecentrifugal force on tip weight 94 will cause release of the weight andconsequent unwinding of the sail rotor blades 76 from the spool 78. Inan alternate form the clamp 98 could be pivoted and weighted such thatinertial forces thereon generated upon rotation of spool 78 would causepivoting thereof to release the associated tip weight 94. In yet anotherform, a solenoidoperated clamp could be utilized to provide more precisecontrol of the release of the tip weight 94.

As mentioned hereinabove, rotation of spool 78 and of shield 86 causesthe release of tip weights 94 which fly out radially to serve indeploying blades 76 by causing unreeling thereof from spool 78. Blades76 are tensioned by the centrifugal force on weights 94 in their endpositions and thus function in the same manner as rigid fan blades. Theblades 76 are shown in the extended, operative positions thereof in FIG.8 with two of the blades being removed for purposes of clarity ofillustration. The actual number of blades utilized is a matter of designalthough FIGS. 6 to 8 are intended to show a fourblade arrangement. Asshown in FIG. 8, the blade angle, that is, the angle between the rotorblade or airfoil section and the plane of rotation, increases along thelength of blade 76 from tip to root. At the tip end of blade 76 thisangle should be small (on the order of 5 or 10 degrees) whereas at theroot end, that is, at spool 78, the angle should be large, with a limit,for large radius blades mounted on small radius hubs, approaching 90.

A clock motor in the form of an elongate coil spring 104 (partiallybroken away in FIG. 6 to show spool 78 and blade 76) surrounding stack70 aids in rewinding the blades onto the spool 78 when the fan 74 is tobe stopped and the blades 76 to be stowed. Spring 104 is connected tothe shield 86 as indicated at 106 and to spool 78 as indicated at 108(see FIG. 7). Spring 104 is loaded such that shield 86 is urged therebyin the same direction as spool 78 rotates. Spring 104 is not fully wounduntil blades 76 are fully extended by weights 94. To stop fan operationand stow blades 76 the drive motor and consequently, the rotation ofspool 78, is slowed down. The inertia of the tip weights 94 will urgeblades 76 forward with respect to spool 78 and thus the blades will tendto wind or wrap themselves around outer shield 86. However, at this timeshield 86 is also being urged forward by the release of the storedenergy in spring 104 as the spring 104 unwinds so that each blade 76will retract through its associated slot 96 in shield 86 and wrap aroundspool 78. The rate at which retraction of the blade 76 takes place iscontrolled by the speed at which the spool 78 is driven and the forceexerted by coil spring 104. At the end of rotation of spool 78 tipweights 94 will be positioned in the openings between springs and 102 ofclamp 98 and the natural inward velocity of the weights will cause theweights to snap into position within clamps 98.

It is noted that for more positive control over reeling and unreeling ofthe blade 76 the shield 86 can be positively driven with respect to thespool 78, A gearing arrangement (not shown) can be employed so that theshield 86 may be driven in the same direction as or in an oppositedirection to the direction in which the spool 78 is driven. In such anarrangement engagement of the drive gears for determining the directionof rotation of the shield 86 can be conveniently controlled throughcontrol of the axial positioning of the gears.

In addition to the advantages in stowing of the blades afforded by thearrangement of FIGS. 6 to 8 this arrangement also permits the use ofblades ofa very large radius, this use, among other advantages, furtheraiding in diffusing of the pollutant plume by providing a more extensiveouter envelope of air.

It is noted that the angle of attack of the blades of the various fanarrangements may be controlled to permit directional control of theplume of pollutant. Reference is made to my copending application Ser.No. 789,328 discussed hereinabove for details of a blade angle controlsystem for a flexible blade arrangement such as that shown in FIGS. 6 to8. By tilting the plane of the blades the plume can be made to flowupwardly from the stack at a favorable angle with respect to the winddirection such that untoward effects of the winds can be reduced byselective orientation of the plume. Further, the stack plume can becontrolled in this manner to aim the plume into the less objectionabledirection.

FIGS. 9 and 10 illustrate a simplified arrangement wherein the directionof the stack plume can be controlled. This arrangement, which isgenerally denoted 106, includes a drive ring 108 which is mounted atop aconventional stack 110 and is adapted to rotate with respect theretothrough upper and lower bearings 112 and 114. A downwardly dependingportion of drive ring 108 has mounted thereon a ring gear 116 (see FIG.10) which is adapted to mesh with a pinion 118 driven by a motor 120.Motor 120 is mounted on stack 110 by means of suitable support membersdenoted 122. It will be appreciated that rotation of motor-driven pinion118 will cause rotation of ring gear 116 and thus ofdrive ring 108.

First and second pins 124 and 126 are affixed to and extend outwardly ofdrive ring 108 on opposite sides thereof as shown. Pins 124 and 126joumaled in and thus provide pivots for an inner gimbal ring 128. Firstand second pins and 132 are affixed to gimbal ring 128 and extendoutwardly therefrom as shown, the axis determined by or common to pins130 and 132 lying perpendicular to the axis determined by pins 124 and126. Pins 130, 132, similarly to pins 124, 126, are joumaled in an outergimbal ring 134 which supports first and second rotor blades 136 and138. Gimbal 134 is connected to blades 136 and 138 through rigid bladeroot or shaft members 140 and 142, respectively, outer gimbal ringserving as a hub as described hereinabove. It will be appreciated thathinged rotor blades such as those shown in FIGS. 4 and 5 could beutilized and that in such an embodiment outer gimbal 138 would serve toanchor the inner hinge in the same way as does hub 30 of FIGS. 4 and 5.

A control ring 144 is positioned adjacent outer gimbal 134 inwardlythereof, outer gimbal 134 being mounted for rotation with respect tocontrol ring 144 by means of a bearing arrangement indicated at 146.Control ring 144 fixedly mounted by first and second control actuators148 and 150 which are affixed to the stack 110 at points located 90degrees apart on the peripheral surface of the stack 110. Actuators 148and 150 include connecting members 148a and 150a which arelongitudinally adjustable to increase or decrease the length of theconnection between the control ring 144 and the stack 110. Increasing ordecreasing the effective length of either of the connecting members148a, 150a from the lengths shown in FIGS. 9 and 10 will result in atilting from the horizontal of outer gimbal 134, and consequently ofblades 136 and 138, through the pivoting arrangement provided by pins124, 126 and 130, 132. Hence the direction of the plume of ambient airand the stack plume which it surrounds can be controlled, throughcontrol arrangement 106, in any direction by controlling the axis ofrotation of the hub 134 and blades 136 and 138.

Referring to FIGS. 11 and 12, there is shown an embodiment of theinvention wherein a fan arrangement is not used. Although one of theembodiments discussed hereinabove is generally to be preferred from aneconomical standpoint, the embodiment of the invention shown in FIGS. 11and 12 is readily adaptable to existing stacks which might notaccommodate a fan-type arrangement.

In FIGS. 11 and 12, a conventional smokestack 160, referred tohereinafter as the primary stack, is positioned centrally of andsurrounded by a concentric secondary stack 162. Primary stack 160 is fedin a conventional manner through a duct 164 so that a plume ofpollutants to be controlled will issue from stack 160 as describedhereinabove. Secondary stack 162 is fed from an air blower arrangement166 through a diffuser 168, the purpose of the diffuser being to improvethe efficiency of the system. A grid structure 170 located in the upperend of secondary stack 162 provides straightening" of the airflow fromthe stack and thus also improves the efficiency of the system. It isnoted that a single secondary stack corresponding to stack 162 can beused in a multiple primary stack arrangement.

It will be appreciated that the operation of the embodiment of FIGS. 11and 12 is similar to that described hereinabove, that is, secondarystack 162 creates an outer plume or jet of air which surrounds the plumeof pollutants issuing from stack 160 to ensure that the plume ofpollutants is carried aloft before diffusing into the atmosphere and toprovide dilution of the pollutants.

It will be understood by those skilled in the art that the embodimentsof the invention shown and described herein are subject to variousmodifications without departing from the scope and spirit of theinvention. Accordingly, it should be understood that the invention isnot limited by the exemplary embodiments shown and described but ratheronly by the subjoined claims as construed in light of the spirit of theinvention.

Having thus described my invention in accordance with the PatentStatutes,

lclaim:

1. In combination with a structure having a stream of pollutants issuingtherefrom, an air pollution control arrangement comprisingpositive-acting antipollution means associated with the structure for,when actuated, actively and continuously providing an envelope ofambient air the cross-sectional area of which is greater than thecross-sectional area of the stream of pollutants and which continuouslysurrounds the stream of pollutants for carrying said pollutants aloft,and means for selectively controlling actuation of said antipollutionmeans.

2. An arrangement as claimed in claim 1 wherein the structure comprisesat least one primary stack and said means comprises a secondary stackfor producing a plume of air surrounding the pollutants issuing from theat least one primary stack.

3. An arrangement as claimed in claim 2 further comprising a blower anda diffuser, said secondary stack further including a flow straighteninggrid.

4. In combination with a structure having a stream of pollutants issuingtherefrom, an air pollution control arrangement comprisin antipollutionmeans associated with the structure for provi mg an envelope of ambientair the cross-sectional area of which is greater than thecross-sectional area of the stream of pollutants and which continuouslysurrounds the stream of pollutants for carrying said pollutants aloft,said antipollution means comprising rotary means including a pluralityof blade members extending outwardly of the structure and lying in agenerally horizontal plane in the operative positions thereof.

5. An arrangement as claimed in claim 1 wherein the struc ture comprisesmeans defining an upwardly extending passage and said blade members arestowable in an inoperative position adjacent said passage-definingmeans.

6. An arrangement as claimed in claim 5 wherein said blade members arehinged to permit movement thereof in a vertical plane and in ahorizontal plane.

7. An arrangement as claimed in claim 6 wherein means are provided fordamping movement of said blade members in a vertical direction and in ahorizontal direction.

8. An arrangement as claimed in claim 4 wherein said blade members areflexible and said rotary means includes spool means on which saidflexible blade members may be wound.

9. An arrangement as claimed in claim 8 wherein said rotary meansincludes means'for rotatably driving said spool means and wherein eachof said flexible blade members includes a tip body located at one endthereof, said rotary means further comprising means for releasablyretaining said blade members in a stowed position wound about said spooluntil the speed of rotation of said spool is such that the centrifugalforces acting on said tip body cause release of said retaining means.

10. An arrangement as claimed in claim 9 wherein said rotary meansfurther comprises a rotatable shield arranged concentrically with saidspool and including slots therein for permitting extensions of saidblade members therethrough and spring means arranged between said shieldand said spool for causing rotation of said shield in the direction ofrotation of said .spool means when said blade members are being unwound,said spring means being wound as said blade members are assuming theoperative positions thereof, the stored energy of said wound springdriving said shield in the same direction as said spool as the speed ofrotation of said blade members is decreased to enable said blade membersto wind themselves around said spool means and to prevent said blademembers form winding themselves about said shield.

11. An arrangement as claimed in claim 4 wherein said blade members areflexible, said blade members being attached at one end thereof to arotary member and at the other end thereof to a tip body.

12. An arrangement as claimed in claim 4 wherein said blade members arerigidly secured to a hub member, said arrangement further comprisingmeans for shielding said blade members from wind effects.

13. An arrangement as claimed in claim 4 further comprising a hub forsupporting blade members and means for controlling the angle between theaxis of rotation of the hub and the axis of the structure to therebycontrol the direction of the plume of ambient air and the plume ofpollutants contained therein.

14. An arrangement as claimed in claim 4 further comprising means forcontrolling the angle of the plane of said blade members with respect tothe horizontal to thereby control the direction of the plume of ambientair and the plume of pollutants contained therein.

1. In combination with a structure having a stream of pollutants issuingtherefrom, an air pollution control arrangement comprisingpositive-acting antipollution means associated with the structure for,when actuated, actively and continuously providing an envelope ofambient air the cross-sectional area of which is greater than thecross-sectional area of the stream of pollutants and which continuouslysurrounds the stream of pollutants for carrying said pollutants aloft,and means for selectively controlling actuation of said antipollutionmeans.
 2. An arrangement as claimed in claim 1 wherein the structurecomprises at least one primary stack and said means comprises asecondary stack for producing a plume of air surrounding the pollutantsissuing from the at least one primary stack.
 3. An arrangement asclaimed in claim 2 further comprising a blower and a diffuser, saidsecondary stack further including a flow straightening grid.
 4. Incombination with a structure having a stream of pollutants issuingtherefrom, an air pollution control arrangement comprising antipollutionmeans associated with the structure for providing an envelope of ambientair the cross-sectional area of which is greater than thecross-sectional area of the stream of pollutants and which continuouslysurrounds the stream of pollutants for carrying said pollutants aloft,said antipollution means comprising rotary means including a pluralityof blade members extending outwardly of the structure and lying in agenerally horizontal plane in the operative positions thereof.
 5. Anarrangement as claimed in claim 1 wherein the structure comprises meansdefining an upwardly extending passage and said blade members arestowable in an inoperative position adjacent said passage-definingmeans.
 6. An arrangement as claimed in claim 5 wherein said blademembers are hinged to permit movement thereof in a vertical plane and ina horizontal plane.
 7. An arrangement as claimed in claim 6 whereinmeans are provided for damping movement of said blade members in avertical direction and in a horizontal direction.
 8. An arrangement asclaimed in claim 4 wherein said blade members are flexible and saidrotary means includes spool means on which said flexible blade membersmay be wound.
 9. An arrangement as claimed in claim 8 wherein saidrotary means includes means for rotatably driving said spool means andwherein each of said flexible blade members includes a tip body locatedat one end thereof, said rotary means further comprising means forreleasably retaining said blade members in a stowed position wound aboutsaid spool until the speed of rotation of said spool is such that thecentrifugal forces acting on said tip body cause release of saidretaining means.
 10. An arrangement as claimed in claim 9 wherein saidrotary means further comprises a rotatable shield arrangedconcentrically with said spool and includIng slots therein forpermitting extensions of said blade members therethrough and springmeans arranged between said shield and said spool for causing rotationof said shield in the direction of rotation of said spool means whensaid blade members are being unwound, said spring means being wound assaid blade members are assuming the operative positions thereof, thestored energy of said wound spring driving said shield in the samedirection as said spool as the speed of rotation of said blade membersis decreased to enable said blade members to wind themselves around saidspool means and to prevent said blade members form winding themselvesabout said shield.
 11. An arrangement as claimed in claim 4 wherein saidblade members are flexible, said blade members being attached at one endthereof to a rotary member and at the other end thereof to a tip body.12. An arrangement as claimed in claim 4 wherein said blade members arerigidly secured to a hub member, said arrangement further comprisingmeans for shielding said blade members from wind effects.
 13. Anarrangement as claimed in claim 4 further comprising a hub forsupporting blade members and means for controlling the angle between theaxis of rotation of the hub and the axis of the structure to therebycontrol the direction of the plume of ambient air and the plume ofpollutants contained therein.
 14. An arrangement as claimed in claim 4further comprising means for controlling the angle of the plane of saidblade members with respect to the horizontal to thereby control thedirection of the plume of ambient air and the plume of pollutantscontained therein.